Producing Nano-Ribbons

Graphene has been recognized for its high strength, conductivity and potential for use in nanoscale devices.

The method created by Yaoyi Li and his team for producing these narrow ribbons could offer new applications in nano-devices. However, before the ribbons can be applied to nanoelectronics, a method for controlling the flow of electrons must be established.

Nano-ribbons are model systems for studying nanoscale effects in graphene, but obtaining a ribbon width below 10 nanometers and characterizing its electronic state is quite challenging.

Yaoyi Li, a UWM physics postdoctoral researcher

Using scanning-tunneling microscopy, the researchers were able to confirm exactly how narrow the ribbons must be to change the electrical properties of graphene and make it more tunable.

We found the transition happens at three nanometers and the changes are abrupt. Before this study, there was no experimental evidence of what width the onset of these behaviors is.

Michael Weinert, UWM theoretical physicist

By making the ribbons narrower, Yaoyi Li and his team were able to confirm that the material becomes more tunable. The narrow ribbons outer edges are able to interact, which essentially transforms the ribbon into a semiconductor with unique tunable abilities similar to those found in silicon.

Making the Cut

Using current cutting methods researchers can achieve ribbon widths of five nanometers - however this is too short to achieve a tunable state. In order to maintain the electrical properties needed, its essential when cutting the ribbons to size that the alignment of the atoms on each edge remains straight.

Image Credit: University of Wisconsin-Milwaukee (UWM) - Yaoyi Li (foreground) and Mingxing Chen, UWM physics postdoctoral researchers, display an image of a ribbon of graphene 1 nanometer wide. In the image, achieved with a scanning-tunneling microscope, atoms are visible as “bumps.”

The iron nanoparticles are free to move across the surface of the graphene, creating ribbons of various widths. This method ensures that the edges have properly aligned atoms.The UWM team used iron nanoparticles placed on top of the graphene in a hydrogen rich environment. The iron causes the hydrogen and carbon atoms to react which in turn creates a gas that etches a trench into the graphene surface. Precisely controlling the hydrogen pressure allowed the researchers to achieve a successful cut.

Creating a Semiconductor

Once the cut has been made the atoms at the edges of each ribbon have only two of the normal three atoms present. This creates a bond which attracts hydrogen atoms and corrals electrons. If the ribbon is narrow enough, the electrons on opposite sides can still interact with each other, creating an electrical behaviour found in semiconductors.

Yaoyi Li and his team are now experimenting with the ribbons by saturating the edges with oxygen to investigate whether this changes the electrical behaviour similar to the characteristics found in some metals.

Looking forward

The method created by Yaoyi Li and his team may yet need some further development, however the technology demonstrates again how versatile graphene can be.

The function created by these nano-ribbons could make atomic-scale components made from the same material a reality, but with a variety of different electrical properties.

Graphene oxide membranes have been receiving attention for their extremely powerful separation abilities and the ease at which it can be modified, allowing for membrane permittivity to be fine-tuned. These membranes show the potential to be used for water purification, ‘green’ gas purification and greenhouse gas capture.